1. Field of the Invention
The present invention relates to a recording apparatus and a recording method, and more particularly, to a technique for correcting an error in an amount of conveyance of a recording medium in an inkjet recording apparatus.
2. Description of the Related Art
In general, a high-precision roller obtained by coating a metal shaft with grinder stone is used as a main conveying roller in an inkjet printer. A position detector (a code wheel and an encoder sensor) provided on the main conveying roller is used to control a DC motor. Accordingly, the inkjet printer is capable of conveying a recording medium (sheet) with high accuracy and high-quality images can be recorded. However, there is a limit to increasing the sheet conveying accuracy by increasing the processing accuracy of the conveying roller. To further increase the sheet conveying accuracy, a correction of eccentricity of the roller has recently been performed.
The correction of eccentricity will be briefly explained. If the cross section of the conveying roller is round and the central axis thereof coincides with the rotation axis thereof, a circumferential length (length of arc) corresponding to a rotation of the roller is constant as long as the rotation angle of the roller for conveying the sheet is constant. Therefore, an amount of conveyance of the recording medium which is conveyed while being in contact with the roller is always constant. However, if the cross section of the conveying roller is elliptical, the amount of conveyance varies in accordance with the rotational position (rotational phase) of the roller even if the roller is rotated by a constant angle. More specifically, an area in which the amount of conveyance is larger than a predetermined amount and an area in which the amount of conveyance is smaller than the predetermined amount are provided in accordance with the rotational phase, and an error in the amount of conveyance varies accordingly. In the correction of eccentricity, a correction value for correcting the amount of conveyance is obtained for each rotational phase of the roller, and the error in the amount of conveyance which varies in accordance with the rotational phase is corrected using the correction value. In the following description, the amount of conveyance obtained by rotating the roller by a predetermined angle is also referred to as a unit amount of conveyance.
An ejection roller is positioned downstream of the conveying roller, and is provided with driven rollers called spurs having a star-like shape with pointed projections to convey a sheet on which ink is applied. The ejection roller is composed of a rubber roller made of an elastic member so that the ejection roller does not damage the projections on the spurs. Therefore, even when the correction of eccentricity is performed for the ejection roller, the sheet conveying accuracy cannot be maintained as reliably as that in the case where the correction of eccentricity is performed for the conveying roller.
The sheet conveying accuracy is particularly affected by the amount of conveyance at the time when the sheet is passed from the conveying roller to the ejection roller. In other words, the sheet conveying accuracy at the time when the state in which the sheet is conveyed by both the conveying roller and the ejection roller is switched to the state in which the sheet is conveyed only by the ejection roller is crucial. In the sheet conveying operation at this time, generally, the sheet conveying accuracy decreases from that in the state in which the sheet is conveyed by both the conveying roller and the ejection roller due to various causes, such as bending of a roller shaft and unstable behavior of the sheet which occurs when the sheet is released from the conveying roller, other than the reduction in the roller accuracy. Accordingly, to suppress the reduction in the sheet conveying accuracy at the time when the sheet is passed from the conveying roller to the ejection roller, Japanese Patent Laid-Open No. 2005-7817 discusses a technique for correcting the amount of conveyance at this time by determining a correction value for the amount of conveyance at this time by using a test pattern.